The present invention generally relates to heat exchangers and, more particularly, to apparatus and methods of using regenerative and ambient flows into heat exchangers.
Many environmental control systems (ECS) utilize “regenerative” flow to cool the cycle operating fluid. Regenerative flow is conditioned air or liquid flow that has been cooled, and then used to perform high-quality (i.e., low temperature) cooling of system heat loads. After the flow has performed this cooling, it is warm, but still cooler than the fluid temperature at the hot portions of the cycle. Because of this, the flow can be used to “self-cool” the cycle hot fluid. After it is thus used, it is then very hot and no longer useful for cooling, and is typically rejected to ambient as waste heat.
To perform this regenerative cooling, heat exchangers are needed. These heat exchangers are often used to supplement other heat exchangers that directly use external ambient fluid (e.g., air, water) to cool the working cycle fluid. By supplementing the main, ambient fluid heat exchangers with the regenerative heater exchangers, it is possible to reduce the size of the main ambient heat exchangers, and the amount of ambient fluid that is used. This offers benefits in terms of system weight and outside power or aerodynamic drag.
At some design conditions, it is common for the regenerative flow to be limited due to the scarcity of working fluid (for example, during low engine settings for cycles using bleed air from jet engines.) At these design conditions, the benefit from the regenerative heat exchangers will be significantly reduced or completely eliminated, which reduces the sizing benefit that can be granted to the other main heat exchangers.
As can be seen, there is a need for improved apparatus and methods for regenerative heat exchange.